The present invention relates to a data storage system, and more particularly, to the detection of data in a system having a shift register storage device.
Semiconductor charge-transfer devices, such as charge-coupled devices (CCD's), are well-known and have been used and proposed for use in various applications relating to the storage of data.
One problem associated with CCD's is the difficulty in reliably and accurately detecting the data stored in the device. A CCD operates much like a serial shift register, with the bits of information represented by charge packets serially shifted through the CCD. During the shifting, the CCD frequently experiences charge losses. The losses are affected by various considerations, and can vary from one device to another. For example, CCD's are sensitive to variations in temperature, clocking frequency and the physical dimensions within the device.
In the past, detection of the data in a CCD has been accomplished by comparing the signal from each cell with an external reference signal. However, if significant cell-to-cell losses occur, such a comparison does not reliably detect the stored data. To minimize cell-to-cell losses it is necessary that there be frequent regeneration of the data and that operating temperatures be kept within specified ranges, among other things. These constraints have increased the cost and physical size of CCD's and thus made them undesirable for many memory applications.